The present invention relates generally to wireless broadcast transmissions and more particularly to a method for power consumption by an IEEE 802.11 client station containing both a Voice-over-Internet Protocol and an Internet Protocol paging application.
An IEEE 802.11 client station having both Voice-over-Internet Protocol (VoIP) and Internet Protocol paging applications must receive unicast VoIP messages, broadcast Address Resolution Protocol, or ARP, messages, and IP Multicast “paging” messages. In a typical computer network, unicast VoIP operation is a communications transmission between a single sender and a single receiver over a network.
In contrast to the unicast transmission of VoIP, paging is typically a multicast operation. Multicast is a technique that allows data, including data encapsulated in packet form, to be simultaneously transmitted to a selected set of destinations. Some networks, such as Ethernet, support multicast by allowing a network interface to belong to one or more multicast groups. In some applications of multicast, identical data is simultaneously transmitted to a selected set of destinations in a network, without obtaining acknowledgement that the transmission was received by the recipient devices. Multicast transmissions are also capable of being sent to a multicast address, which is typically a routing address that is used to address, i.e., designate, simultaneously all the computers in a group and usually identifies a group of computers that share a common protocol, as opposed to a group of computers that share a common network.
Thus, while multicast has a single sender and multiple recipients, unicast has but a single sender and a single recipient. Similar to multicast, broadcast operation is the transmission of signals that may be simultaneously received by stations that typically make no acknowledgement of the receipt of the transmission.
Address Resolution Protocol is a communications protocol used to map a selected Internet Protocol (IP) address to a preset Media Access Control (MAC) address. ARP matches higher-level IP addresses to the physical addresses of the destination host. It uses a lookup table (called an ARP cache) to perform the translation. When the address is not found in the ARP cache, a broadcast is sent out on the network with a special format called the ARP request. If one of the machines on the network recognizes its own IP address in the request, it sends an ARP reply back to the requesting host. The reply contains the physical hardware (MAC) address of the receiving host. The requesting host stores this address in its ARP cache so that all subsequent datagrams to this destination IP address can be translated to a physical address.
A Traffic Indication Message (TIM) may be found in an 802.11 Beacon Frame which is transmitted from an 802.11 access point (AP). In essence, a TIM is used by access points to tell power-save client devices that one or more unicast packets are waiting for them. A TIM consists of an array of bit flags, with one bit flag for each client associated with the AP. An AP sets a station's TIM bit to “1” if it has one or more frames buffered for the client. An AP sends Beacons at fixed intervals. If an 802.11 power-save station only needs to receive unicast frames, it can wake up to receive a Beacon, check its TIM bit, and immediately return to a “sleep” mode if the TIM bit is set to “0”.
A Delivery Traffic Indication Message (DTIM) is contained in DTIM Beacons sent by access points. If a power-save station associated with an AP, then the AP buffers broadcast and multicast frames and sends the buffered frames to associated stations immediately following a DTIM Beacon. If a power-save station must receive broadcast or multicast frames, then it must wake up for each DTIM Beacon transmission and it must stay awake until the last broadcast/multicast frame is transmitted, following the DTIM Beacon.
Proxy ARP refers to a method wherein an AP sends an ARP Reply, on behalf of an associated station, when the AP receives and ARP Request directed to the associated station. Proxy ARP enables a power-save station to sleep during the broadcast/multicast period, following a DTIM Beacon, if it does not need to receive any of other multicast or broadcast frames.
Previous attempts to implement proxy ARP 802.11 VoIP phone applications have been met with limited success. Such uses of the proxy ARP has enabled the VoIP phone to sleep, or operate in power-save protocol mode, during lengthy broadcast/multicast transmissions. However, this mechanism, by itself, is not usable for an 802.11 VoIP/Paging device insofar as the paging application requires the phone to remain active following the DTIM to receive other multicast transmissions.
A problem associated with an 802.11 client device supporting both VoIP and paging applications is that the radio power consumption in an 802.11 VoIP phone is much higher than the radio power consumption in a cellular telephone. The greater drain on energy has limited the application of both VoIP and paging into a single device. Power-save stations must stay awake, for the duration of the multicast delivery period, to receive multicast transmissions. As a result, broadcast/multicast transmissions can reduce battery life in power-save stations.
Thus, there exists a need for a system and method to provide an effective power-save solution for combined VoIP/paging applications.